Macronutrient, immunoglobulin A and total antioxidant capacity profiles of human milk from 1 to 24 months postpartum

Background: A longer duration of breastfeeding of up to two years is encouraged by many health authorities, but there is limited information regarding the composition of milk after one year postpartum. The goal of this study was to determine the changes in human milk macronutrient, immunoglobulin A (IgA), and total antioxidant capacity (TAC) profiles during extended lactation.Methods: One hundred eighty-four breastfeeding mothers with full-term healthy children who had been lactating from 1 to 24 months were recruited from January 2019 to April 2019. Human milk was biochemically analyzed for protein and carbohydrate content by colorimetric assays. The fat content was determined by capillary centrifugation, and the energy content was calculated from the results of centrifugation assays. IgA levels and TAC were determined by ELISA and a Trolox equivalent antioxidant capacity (TEAC) assay, respectively. Pearson’s correlation coefficient and Spearman’s rank correlation coefficient were used to determine the association of milk composition with month of lactation.Results: The fat, energy and IgA contents were positively correlated with the duration of lactation (r = 0.229, p = 0.002 ; r = 0.229, p =0.002 and r = 0.304, p < 0.001, respectively). No significant correlations between protein, carbohydrate concentrations and TAC with the duration of lactation were observed (r = 0.106, p = 0.15; r = -0.032, p = 0.67; r = -0.056, p = 0.45, respectively).Conclusions: We demonstrated that fat, energy and IgA contents increased during extended lactation lasting up to two years postpartum, while protein and carbohydrate concentrations and TAC were not related to lactation duration. Based on these results, lactating mothers should be encouraged to continue breastfeeding for at least two years postpartum.